Accelerated heavy ions have physical properties and biological consequences that make them ideal candidates for the radiotherapeutic treatment of tumors. The physical properties include high Linear Energy Transfer (LET) especially at the end of the track, a favorable depth-dose distribution, and an easily localized and collimated beam. The favorable biological consequences include the low Oxygen Enhancement Ratio (OER) and the high Relative Biological Effectiveness (RBE) resulting in efficient killing of malignant tissue. Little is known about the nature of damage induced in cells by accelerated heavy ions. These experiments are designed to give basic information about the sensitivity of proliferating and non-proliferating cells to damage by heavy ions affecting cell survival, clonogenicity, and mutation induction. The kinetics of induction of damage by 15Mev neutrons, 4He, 12C, 20Ne, and 40Ar and the affect of LET on the RBE calculated for these parameters will be determined. Survival and clonogenicity will be measured in germ cells of the mouse, and the mutagenic consequences will be measured as dominant lethal mutations expressed by mouse embryos grown in vitro from the 2-cell stage to an early implantation stage. It is anticipated that these studies will contribute to a pre-clinical evaluation of the radiotherapeutic potential of accelerated heavy ions, will aid in our understanding of the process of mutation induction and expression in mammals, and will evaluate a mammalian test system for screening carcinogens whose action may be mechanistically related to damage by High LET particles.